Generally, active and extensive collagen turnover is not considered a prominent feature in healthy adults. Turnover of collagen type II, a component of articular collagen, generally occurs in diseases, such as rheumatoid arthritis, osteoarthritis or other diseases or physiological conditions in which collagen degradation is a factor.
The breakdown of collagen type II is believed to be initiated by specific members of the matrix metalloproteinase family of enzymes, the collagenases. Collagens are comprised of three peptide strands wound in a helix formation. For example, collagen type II is comprised of a triple helix of three identical peptide strands referred to as peptide alpha 1, collagen type II (SEQ ID NO: 44). When collagen is degraded or cleaved by a collagenase, the cleavage takes place at a specific intra-helical site leaving the peptides vulnerable to further degradation or cleavage. In any event, the initial cleavage results in the generation of collagen fragments having an end defined by the proteolytic cleavage. For example, collagenase degradation of collagen type II results in a peptide fragment having the C-terminal sequence ending with: GPXGPQG, where X is proline or hydroxyproline. Billinghurst et al described this primary collagenase cleavage site and developed antibodies reactive to both the carboxy-terminal and amino-terminal “neoepitopes” generated by cleavage of native human collagen type II. (J. Clin.Invest. 99:1534–1545 (1997)). Otterness et al have described production of a monoclonal antibody directed against this carboxy-terminal “neoepitope” (Matrix Biology 18: 331–341 (1999)).
U.S. Pat. No. 6,030,792 to Otterness et. al. discloses antibodies for detecting collagen fragments resulting from collagenase cleavage of type II collagen. Poole et al. U.S. Pat. No. 6,132,976 provides a method for evaluating cartilage degradation by immunoassay measurement of type II collagen cleavage. In any event, the prior art methods for the detection of collagen type II enzymatic cleavage by detecting the presence of peptide fragments only determine the presence of the target C-terminus portion and immediately adjacent peptide sequence using antibodies specific for these sequence regions.